Actuator

ABSTRACT

In actuators where an electric motor, via a transmission, drives an activation element intended to cause movement of an adjustable element in the structure in which the actuator is incorporated, particularly within the furniture sector, hospital beds and sickbeds. The level of noise may be reduced in that at least the electric motor ( 6 ) is mounted in tightly fitting recess ( 12 ) in a block ( 11 ) of foam plastics or similar vibration/noise damping material. An additional reduction of vibrations/noise is achieved by inserting a claw coupling ( 9   a,    9   b ) with a gasket of rubber or rubber-like material between the individual claws in the claw coupling.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an actuator that includes a cabinet, anelectric motor arranged in the cabinet, the motor having a motor shaft,a transmission connected to the motor shaft, the transmission having anoutput stage, and an activation element connected to the output stage ofthe transmission, the activation element being intended to causemovement of an adjustable element in the structure in which the actuatoris incorporated.

2. The Prior Art

Actuators driven by a reversible low volt DC motor, typically 24V, areused for adjustable articles of furniture, such as beds, chairs andtables. In a linear actuator, the motor, via a transmission, drives aspindle having a nut fixed against rotation so that the nut can move toand fro on the spindle depending on the direction of rotation of thespindle. The nut has arranged thereon a tubular rod whose free end isprovided with an attachment for securing in the structure. Typically,the transmission simply consists of a worm gear, where the worm isprovided in extension of the motor shaft and the worm wheel secureddirectly on the spindle. An example is disclosed in WO 02/29284 to LinakA/S. A special structure of linear actuators is called lifting columns,e.g. intended as table legs. Rotary actuators have so far not been ascommon as linear actuators in connection with furniture, but a singleexample based on a specially constructed planetary gear is described inWO 01/17401 to Linak A/S. In the furniture business, the price of theactuators is a decisive factor, which has become particularly pronouncedrecently. This, of course, has resulted in a development toward simplerstructures. In the furniture business in particular, an essential aspectis the level of noise, and with a demand for less expensive actuators,it is even more difficult to meet the requirement for low level noise.

During adjustment of the article of furniture, mechanical noise occurs,such as transmission noise, noise in the suspension of the adjustableelement, noise because of vibrations that propagate in the structure,etc. When the most powerful single sources of noise have been remedied,it is a complex noise picture that emerges, it being very difficult, itnot impossible, to locate the individual sources of noise.

In case of furniture, the level of noise is a significant factor in thesense that this must be as low as possible. This applies to beds,including hospital beds and sickbeds, as well as armchairs and tables,including desks. In the furniture structure and in the drive unit,various common noise-reducing measures may be taken, such as the use ofrubber/plastics suspensions, plastics bushings, lubricants, etc. tocounteract the noise, but in spite of this it is still desirable toreduce the level of noise additionally.

Some of the noise originates from the motor, where part of the noise iscaused by the structure of the rotor with axis-parallel air gaps betweenthe iron flanges on which the coils are wound. This gives small, butnoticeable discontinuities in the magnetic field that cause vibrationswhich propagate in the structure and cause acoustic noise. To obviatethe discontinuity, it has been proposed to twist the armature so thatthe air gap is not axis-parallel. The phenomenon is described in anotherconnection in U.S. Pat. No. 4,616,151 to General Motors Corporation.

Another part of the noise from the motor is caused by an axial movementof the rotor, which likewise results in vibrations and thereby acousticnoise. Owing to manufacturing tolerances it is difficult to do anythingabout the problem. The phenomenon is also described in anotherconnection inter alia in U.S. Pat. No. 5,497,039 to General ElectricCompany and U.S. Pat No. 6,069,422 to Fasco Industries, Inc., both ofwhich propose solutions for fixing the rotor in the axial direction viathe magnetic fields of the stator.

Another aspect of the acoustic noise is the transmission noise, part ofwhich originates from the engagement between the gear wheels or moreparticularly the varying degree of the engagement. In this context,reference is made to WO 01/94732 A1 to VKR Holding A/S, which addressesnoise problems in relation to window openers, focus being on noisecaused by clearance between the components of the transmission, it beingattempted to reduce the noise by controlled engagement between a wormand a worm wheel.

The outlined solutions are expensive and complicated or cannot readilybe implemented in the present connection.

The invention is based on an ever increasing wish for reducing the noiselevel of linear actuators, bearing in mind that this must not lead toincreased or noticeably increased costs.

SUMMARY OF THE INVENTION

This is achieved according to the invention in that the electric motoris mounted in a tightly fitting recess in a block of foam plastics orsimilar material arranged and secured in the cabinet. The foam plasticsserve as a vibration and noise damper, and the foam plastics mayadditionally be given specific properties for a specific type of motorand transmission for maximum vibration/noise damping. In those caseswhere part of or the entire transmission is built together with themotor as a unit, the foam plastics block is expediently shaped so thatthe entire unit is received in its recess. The motor may be secured inthe cabinet by traditional means, but if the structure otherwise sopermits, it is expedient to shape it such that the motor is exclusivelysecured in the foam plastics block, which partly saves the traditionallysecuring means and partly provides for easy mounting of the motor whenit is just to be arranged in the foam plastics block. When, thus, themotor is exclusively secured and enclosed in the foam block togetherwith the transmission, the motor and transmission vibrations are ideallycaptured in the foam plastics and are not transferred to the cabinet.The heat generated by the motor, the transmission and possibly the brakeis transferred to the cabinet. The foam block thus does not result inoverheating of the motor part, but if it is desired to keep thetemperature down, the foam plastics between the motor and the cabinetmay be made thin at strategic locations to facilitate the heat transfer,but there is also the option of inserting heat conductive metalfoils/sheets in the foam block out to the cabinet.

Expediently, the foam plastics block fills the interior of the cabinetentirely or substantially entirely, which results in easy mounting andsimultaneously avoids resonance cavities and thereby contributesadditionally to the vibration/noise damping. The foam plastics block maybe composed of several parts, e.g. two parts with an assembling face inthe longitudinal plane of the motor, preferably so that the motor may bearranged down in the recess on the one part and then the other part isarranged thereon. For mounting and manufacturing purposes it isexpedient with a foam plastics block as one entity with a recess for themotor, said recess having an opening extending out to one end or sidefor insertion of the motor into the block.

In an embodiment of the invention, a claw coupling is present in thetransmission or between the transmission and the activation element ofthe actuator, which makes the assembly particularly easy. The motorunit, i.e. motor with transmission part, may then merely be arrangedwith its part of the claw coupling loosely in the other part of the clawcoupling. In a particularly expedient embodiment, a gasket of rubber orsimilar material is provided between the individual claws of the clawcoupling. This ensures that vibrations/noise from the motor unitpropagate/s into the structure, which additionally ensures that thestructure is comparatively noiseless. The rubber or rubber-like materialof which the gasket is made may also be given specific properties with aview to absorbing the vibrations that occur in the structure concerned.

An exemplary embodiment of the invention will be explained more fullybelow with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a linear actuator in the form of a lifting column,

FIG. 2 shows a drive unit for the lifting column of FIG. 1,

FIG. 3 shows a drive unit for the lifting column of FIG. 1, intended forsynchronous extension of the members,

FIG. 4. shows an exploded view of a cabinet of the actuator,

FIG. 5 a shows the spindle part of the drive unit of FIG. 2,

FIG. 5 b shows a longitudinal section in the spindle part of FIG. 5 a,

FIG. 5 c shows the spindle part of FIG. 5 a, seen directly from above,

FIG. 5 d shows a detail of the upper end of the spindle part,

FIG. 6 a shows the spindle part of the drive unit of FIG. 3,

FIG. 6 b shows a longitudinal section in the spindle part of FIG. 6 a,

FIG. 6 c shows the spindle part of FIG. 6 a, seen directly from above,and

FIG. 6 d shows a detail of the upper end of the spindle part.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 of the drawing shows a linear actuator in the form of a liftingcolumn for height adjustable (sitting/standing) tables with threemembers 1, 2, 3 arranged telescopically inside each other, where theouter member 1 is intended for attachment in a foot at its lower end. Onthe upper end of the inner member 3 there is a cabinet 4 which extendsperpendicularly from the wide side of the column. The sides and the endof the cabinet facing away are formed with holes 5 for the mounting ofthe tabletop/the frame which carries the tabletop. A bracket 1′ for themounting of a rim is provided on the wide side, at the top of the outermember 1. The column may be configured with a non-guided or a guidedintermediate member 2. In case of a non-guided member 2, the innermember 1 is pushed out first, following which the intermediate member 2is carried along via engagement. Owing to friction between theindividual members, however, the movement of the intermediate member 2may be more or less arbitrary. FIG. 2 shows a drive unit for non-guidedmovement of the intermediate member, and FIG. 3 shows a drive unit forsynchronous movement of the inner and intermediate members 1, 2.

FIG. 4 shows an exploded view of the cabinet 4, which is of deep-drawnsteel here. The motor unit 10 comprises a DC motor 6 having two plane,parallel sides. The front end of the motor includes a front bracket 7 ofmetal with a worm wheel (transmission) 8 in engagement with a worm,which is formed by an extension of the motor shaft. A screw spring 14serving as a brake is mounted on the upwardly-facing side of the frontbracket, cf. Danish Patent Application PA 2003 01650 to Linak A/S. Onepart of a claw coupling 9 a is mounted on the downwardly facing side ofthe worm wheel 8.

The cabinet 4 accommodates a block of foam plastics 11, e.g.,polyurethane, with a recess 12 for the motor part 1. The recess isconfigured tightly-fitting as far as the motor 6 itself and theadjoining part of the transmission are concerned. The worm wheel 8 isarranged here in front of the block. The foam plastics block fits snuglyin the cabinet, i.e., fills the hollow of the cabinet where the block isarranged. Prior to the insertion of the foam plastics block, the motorpart with the motor itself is moved into the recess that terminates atthe front end of the block. Finally, a plastics cover 13 is mounted,having snap locking legs which engage recesses in the sides and ends ofthe cabinet intended for the purpose. Thus, the motor part is loose,exclusively enclosed in the foam block. The vibrations originating frommotor and transmission are absorbed in the foam plastics and are nottransferred to the cabinet. Thus, the foam plastics serves as avibration and noise damper. The heat generated by motor and brake istransferred to the cabinet, there being an open space between theplane-parallel sides of the motor and the cabinet. As might have beenexpected, the foam block does not cause overheating of the motor part.

FIGS. 5 a-5 d show the spindle part of the drive unit in FIG. 2. Thespindle part comprises an outer pipe 14 whose lower end is secured atthe bottom of the outer member 1. A sleeve with interior threads for ahollow spindle 15 is secured at the top of the pipe 14, and also asleeve with interior threads for a solid spindle 16 is secured at thetop. A ball bearing 17 surrounded by a bearing bush 18 is secured on theend of the Solid spindle 16. The other part 9 b of the claw couplingintended for engagement with the claw 9 a on the motor unit is securedright out on the outer end of the solid spindle 16. A star-shapedelement 19 of rubber is embedded in the other end 9 b of the clawcoupling so as to be disposed with the radially protruding arms betweenthe claws of the two coupling parts. That is that the transfer of forcebetween the two coupling parts 9 a, 9 b takes place via the rubbergasket 19, thereby ensuring completely or partially thatvibrations/noise are/is passed from one part to the other, just as therubber element absorbs irregularities in the connection.

The attachment to the cabinet 4 is carried out by a plate element 20which is internally screwed firmly on to the bottom of the cabinet bytwo screws 21 a, 21 b through screw holes. The bottom of the housing isformed with a hole through which the bearing bushing is seated so thatit is fixed with a four-sided flange between the inner side of thebottom and the plate element 20, which serves as a compressive safeguardfor the load from the tabletop, while the bearing housing serves as atensile safeguard.

FIGS. 6 a-6 d show the spindle part of the drive unit in FIG. 3 forsynchronous guiding of the inner and intermediate members 2, 3. Thespindle part comprises a drive pipe 22, a hollow spindle 23 and a solidspindle 24, secured with the lower end at the bottom of the outer member1. An end element 25 is provided at the lower end of the drive pipe 22,having a passage with interior threads for the hollow spindle 23. Theend element 25 fits in the lower end of the inner profile 3. The innerand intermediate members 3, 2 have interposed between them a frame withslides of plastics secured with pins in holes on the side wall of theinner member 3. The pins have been made so long that they are seated inholes 25 a in the end element 25 for securing of this. A bushing 26 issecured at the upper end of the hollow spindle 23 and has protrudingfins in engagement with grooves (splined connection) on the inner sideof the drive pipe 22. Rotation of the drive pipe 22 will cause thehollow spindle 23 to be screwed out through the end element 25.

An end element 27 with a bearing 28 for the hollow spindle is secured tothe lower end of the hollow spindle 23. The end of the hollow spindlehas a sleeve 29 with threads in engagement with the solid spindle 24.When the hollow spindle rotates, it will screw itself up the solidspindle, while screwing itself out of the drive pipe, for which purposesthe hollow spindle/solid spindle are provided with right-handed andleft-handed threads, respectively. The end element 27 is secured inmanner similar to the one described above with pins from slides, nowbetween the intermediate member and the outer member 2, 1. Since theintermediate member 2 is secured to the lower end of the hollow spindle23 via the end element, it is forcibly moved together with this, in amanner similar to what is shown and described e.g. in DE 39 10 814 toSMS Hasenclever GmbH, cf. FIG. 7B in particular, as well as FR 2 625 488to ZW Hydraulik AG.

The upper end of the drive pipe 22 has secured thereto the other part 9b of the claw coupling intended for engagement with the part 9 a fromthe motor unit 10. The claw coupling part 9 b is secured to the drivepipe via an end plug 30 therein, said end plug having a spline forcooperation with the spline internally in the drive pipe. The end plughas a groove with a toothing on a protruding part, and the coupling part9 b has a corresponding ring wall 31 with a toothing that fits therewithfor rotation-transferring interconnection. The coupling part isadditionally secured by a centre screw in the end plug of the drivepipe.

In the same manner as before, a star-shaped element 19 of rubber isembedded in the other part 9 b of the claw coupling so that it isdisposed with the radially protruding arms (here six arms) between theclaws of the two coupling parts, each of which has three claws. FIG. 6 cshows the three claws from the spindle part, while the further spacesare intended to receive the three claws from the claw coupling part 9 aof the motor part.

The attachment of the spindle part to the cabinet 4 is carried out heretoo with a plate member 20 which is internally screwed firmly on to thebottom of the cabinet by two screws through screw holes 21 a, 21 b. Itwill be appreciated that the drive pipe is secured in the axialdirection between the end element 25 secured in the inner member 3 andthe collar on the plate member 20 secured to the cabinet, which ismoreover welded to the inner member 3.

Although the invention has been illustrated here in connection with anactuator constructed as a lifting column for height-adjustable tables,it will be appreciated that the invention is not restricted to this.Mounting of the motor in a foam plastics block in the cabinet and use ofa claw coupling with rubber gasket may be used to advantage in otheractuators, of course, and just to mention an example, linear actuatorsfor adjustment of hospital beds and sickbeds or beds for domestic use.

1. An actuator comprising a cabinet; a foam plastic block contained inthe cabinet, said foam block defining a recess therein; and an electricmotor tightly positioned in the recess of said foam block, said motorhaving a motor shaft, a transmission connected to the motor shaft, saidtransmission having an output stage, an activation element connected tothe output stage of the transmission, said activation element beingintended to cause movement of an adjustable element in a structure inwhich the actuator is incorporated.
 2. The actuator according to claim1, wherein at least a part of the transmission is built together withthe motor, and this part of the transmission is likewise accommodated inthe recess in the foam plastic block.
 3. The actuator according to claim1, wherein the foam plastic block fills an interior of the cabinetentirely or substantially entirely.
 4. The actuator according to claim1, wherein the foam plastic block is composed of two parts with anassembling face in a longitudinal plane of the motor.
 5. The actuatoraccording to claim 1, wherein the foam plastic block is one piece, andthe recess has an opening extending out to an outer side of the blockfor insertion of at least the motor.
 6. The actuator according to claim1, wherein a claw coupling is arranged in the transmission or betweenthe transmission and the activation element of the actuator.
 7. Theactuator according to claim 6, wherein a gasket of rubber is providedbetween the individual claws of the claw coupling.
 8. The actuatoraccording to claim 6, wherein the two parts of the claw coupling havethree axially extending claws each, and the gasket has six protrudingflaps from a central ring wall or solid core.
 9. The actuator accordingto claim 1 including a spindle part, and one end of the claw coupling issecured to the end of the spindle part.
 10. The actuator according toclaim 1 including a spindle part with a drive pipe for rotation of aspindle, and the claw coupling is secured to one end of the drive pipe.11. The actuator according to claim 9, wherein the spindle part issecured to the cabinet by means of a plate member screwed firmly on tobottom of the cabinet.